I have a question I hope someone can answer. My husband Mark has ALS now for 8 years. He uses Bipap all night and sometimes during the day. Last clinic his PFT's went down. In one month they went from 34 to 25. His 02 levels are good. My question is how long before his 02 levels become effected? His left diaphram is no longer working and his left lung ic collapsed. His right lung is good. Last Dec he had a bad case of pneumonia and we almost ost him. He is not going to vent. Can anyone give some kind of info as what to expect?